The compiler can't find the method repaint(). Where is it defined in your code?
There is a repaint() method defined in the Component class. Does your Left class extend Component or any derivatives of it? It only implements Runnable, so it won't get ANY of Component's methods.
There are some code examples on this forum that will show you how to use paint() and repaint(). Use search. Rewrite your code and come back again later if you have problems. Good luck.